1. Field of the Invention
The invention relates to a liquid crystal display device and a method of fabricating the same, and more particularly to an in-plane switching mode liquid crystal display device and a method of fabricating the same.
2. Description of the Related Art
A method of fabricating a liquid crystal display device usually includes a step in which patterns have to be overlapped each other without misregistration.
For instance, a gate electrode, a source electrode and a drain electrode all to be formed on a thin film transistor (TFT) substrate are usually formed in a multi-layered pattern. In such a multi-layered pattern, misregistration in overlapping a lower layer pattern of which a gate electrode is comprised and an upper layer pattern of which source and drain electrodes are comprised each other has to be quite small.
Similarly, when a plurality of patterns is to be formed in a common layer, misregistration in a boundary at which adjacent patterns are contiguous to each other has to be quite small.
In addition, a difference between an actual dimension of a pattern having been actually formed in a photolithography step and a dimension defined by a mask, that is, a designed dimension has to be equal to or smaller than a threshold.
Since it is almost impossible to accurately measure the above-mentioned misregistration and difference in dimensions after a liquid crystal display device has been fabricated, a vernier is frequently used for indirectly measuring the misregistration and difference.
For instance, Japanese Unexamined Patent Publication No. 6-75243 has suggested a liquid crystal display device including a vernier pattern for measuring the above-mentioned misregistration and difference in a display area.
A liquid crystal display device may be grouped into a first type in which molecular axes of aligned liquid crystal molecules are rotated in a plane perpendicular to a substrate to display a certain image, and a second type in which molecular axes of aligned liquid crystal molecules are rotated in a plane parallel with a substrate to display a certain image. Herein, a direction of axes of aligned liquid crystal molecules is called a director.
A typical one in the first type is a twisted nematic (TN) mode liquid crystal display device, and the second type is called an in-plane switching (IPS) mode liquid crystal display device.
Since a viewer looks only at a direction in which minor axes of liquid crystal molecules extend, even if he/she moves his/her eye point, in an IPS mode liquid crystal display device, how liquid crystal molecules stand is not dependent on a viewing angle, and accordingly, an IPS liquid crystal display device can present a wider viewing angle to a viewer than a TN mode liquid crystal display device.
Hence, an IPS mode liquid crystal display device has been more popular these days than a TN mode liquid crystal display device.
In an in-plane switching (IPS) mode liquid crystal display device, it is necessary to accurately control a width of a line of which an electrode is comprised. If such a line had a width much different from a designed width, a liquid crystal display device would have deteriorated uniformity in a brightness in a display area, or a liquid crystal display device could not have an electric field having an optimal intensity, resulting in deterioration in a brightness.
For instance, in a TN mode liquid crystal display device, a line of which an electrode is comprised is required to have a width controlled at an accuracy in the range of xc2x11.5 to 2.0 micrometers, whereas, in an in-plane switching mode liquid crystal display device, a line of which an electrode is comprised is required to have a width controlled at an accuracy in the range of xc2x10.2 to 0.3 micrometers.
An underlying film to be formed below an electrode in a liquid crystal display device is usually composed of inorganic or organic material. As mentioned above, a line of which an electrode is comprised in an in-plane switching mode liquid crystal display device is required to have an accurately controlled width. An organic film usually discharges gas when an ITO film is formed by sputtering. An etching rate of an electrode formed on an organic film is greater than an etching rate of an electrode formed on an inorganic film. Accordingly, it is more difficult to control a line width of an electrode formed on an organic film than to control a line width of an electrode formed on an inorganic film.
Japanese Unexamined Patent Publication No. 8-106100 (A) has suggested a method of fabricating a liquid crystal display device including two transparent substrates, and a liquid crystal layer sandwiched between the transparent substrates. In the suggested method, a transparent electrode and a scale are formed on at least one of upper and lower surfaces of the transparent substrates, and then, the transparent substrate are adhered to each other through sealing material coated at a periphery of the transparent substrates. When necessary, a line width of the sealing material is measured by means of the scale.
Japanese Unexamined Patent Publication No. 9-258265 (A) has suggested a liquid crystal display device including two electrically insulating substrates, and a liquid crystal layer sandwiched between the electrically insulating substrates. One of the electrically insulating substrates are formed a plurality of switching devices arranged in matrix, first and second wirings electrically connected to the switching devices, an interlayer insulating film covering the first and second wirings therewith and having an upper surface and an inclining surface, and first and second electrodes one of which is electrically connected to the switching devices, for applying an electric field to the liquid crystal layer. The first and second electrodes cover the upper and inclining surfaces of the interlayer insulating film to thereby apply the electric field to the liquid crystal layer in parallel with the electrically insulating substrates.
ITO etching shift characteristics on an organic insulating film is discussed by Y. Kataoka et al. in ISSN 1083-1312/00/2001, pp. 123-126.
However, the above-mentioned problem remains unsolved in those Publications.
In view of the above-mentioned problems in the conventional in-plane switching mode liquid crystal display device, it is an object of the present invention to provide an in-plane switching mode liquid crystal display device including an inorganic film and an organic film as underlying films to be formed below an electrode which device is capable of accurately controlling a line width of an electrode formed on those inorganic and organic films.
It is also an object of the present invention to provide a method of fabricating such an in-plane switching mode liquid crystal display device.
In one aspect of the present invention, there is provided an in-plane switching type liquid crystal display device including (a) a first film composed of inorganic material, (b) a second film composed of organic material, both of the first and second films being to be formed below an electrode as underlying films, (c) a first vernier formed on the first film for measuring a width of the electrode, and (d) a second vernier formed on the second film for measuring a width of the electrode.
The in-plane switching type liquid crystal display device in accordance with the present invention includes the first and second verniers formed on the first and second films, respectively. Hence, it is possible to measure a line width of an electrode formed on the first film and a line width of an electrode formed on the second film independently of each other, and thus, it is possible to control a line width of the electrodes. This ensures enhancement in a fabrication yield of an in-plane switching type liquid crystal display device.
The first vernier may be designed to have a centerline extending in the same direction as a direction in which a centerline of the second vernier extends.
For instance, each of the first and second verniers may be comprised of a metal film including (c1) a plurality of first metal linear regions extending in a first direction and arranged in a second direction perpendicular to the first direction such that the first metal linear regions are equally spaced away from one another, (c2) a plurality of second metal linear regions extending in the first direction and arranged in the second direction such that the second metal linear regions are equally spaced away from one another, (c3) a plurality of first slits extending in the first direction and arranged in the second direction such that the first slits are contiguous to the first metal linear regions, and (c4) a plurality of second slits extending in the first direction and arranged in the second direction such that the second slits are contiguous to the second metal linear regions. A first metal linear region located at an end has a first width equal to a width of the electrode to be measured, and a first metal linear region located remoter from the end has a width equally smaller than the first width. A second metal linear region located at the end has the first width, and a second metal linear region located remoter from the end has a width equally greater than the first width. The first and second slits commonly have the first width.
The metal film may be composed of indium tin oxide (ITO).
The electrode may be composed of electrically conductive transparent material such as indium tin oxide (ITO).
There is further provided an in-plane switching type liquid crystal display device including (a) a first film composed of organic material, and formed below an electrode in a display area as an underlying film, (b) a second film composed of inorganic material, and formed below an electrode in a terminal area extending around the display area, (c) a first vernier formed on the first film for measuring a width of the electrode, and (d) a second vernier formed on the second film for measuring a width of the electrode.
The in-plane switching type liquid crystal display device in accordance with the present invention includes the first vernier formed on the first film in a display area and the second vernier formed on the second film in a terminal area. Hence, it is possible to measure a line width of an electrode formed on the first film and a line width of an electrode formed on the second film independently of each other, and thus, it is possible to control a line width of the electrodes. This ensures enhancement in a fabrication yield of an in-plane switching type liquid crystal display device.
In another aspect of the present invention, there is provided a method of fabricating an in-plane switching type liquid crystal display device, including the steps of (a) forming a first film composed of inorganic material, on a substrate, (b) forming a second film on the first film in a display area of the liquid crystal display device, the second film being composed of organic material, (c) fabricating a first vernier on the first film in a terminal area extending around the display area, for measuring a width of an electrode, (d) fabricating a second vernier on the second film for measuring a width of the electrode, and (e) forming the electrode on the first and second films.
In the method of fabricating an in-plane switching type liquid crystal display device, in accordance with the present invention, the first vernier is formed on the first film in a display area and the second vernier is foxed on the second film in a terminal area. Hence, it is possible to measure a line width of an electrode formed on the first film and a line width of an electrode formed on the second film independently of each other, and thus, it is possible to control a line width of the electrodes. This ensures enhancement in a fabrication yield of an in-plane switching type liquid crystal display device.
The first and second verniers may be formed in separate steps, or may be formed in a common step. Specifically, the above-mentioned steps (c) and (d) may be carried out separately or concurrently.
It is preferable that the second vernier is fabricated in the step (d) such that it has a centerline extending in the same direction as a direction in which a centerline of the first vernier extends.
The above and other objects and advantageous features of the present invention will be made apparent from the following description made with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings.